I. Field of the Invention
The present invention relates generally to concrete batching operations and, particularly, to advances in equipment, and in a method of processing or batching the ingredients used to produce concrete mixes. Specifically, this invention encompasses a batching operation that includes a pre-mix system which measures and controls both the water and the cementitious material feeds in relation to each other so as to be able to blend these components in a known, selected, adjustable and repeatable manner that optimizes the water/cement ratio and therefore the production and strength of the concrete mixture for each mix design. The pre-mix system further includes a twin screw agglomerator pre-mixing unit for blending or pre-mixing these materials prior to combining them with aggregates in a drum of a transit mixer truck or other final mixing vessel.
II. Related Art
In a typical concrete batching operation, all the ingredients are pre-measured and then all the ingredients are transferred to a mobile concrete mixing truck for mixing and transport to job sites remote from the sources of the concrete ingredients. In some batching operations, all the ingredients may be transferred to a pre-mixer, which is a permanent part of the batching operation, before being transferred to a mobile concrete mixing truck or other receiving vehicle.
Pre-mixing of the water and cementitious materials prior to bringing them together with the aggregates is known to offer several advantages. These advantages include, but are not limited to:                1. Increased concrete strength results from improved hydration of the cementitious materials.        2. Cost savings result from increased concrete strength when the concrete producer is supplying a strength based concrete.        3. Improved truck utilization is possible due to faster loading of agglomerated mixes into mobile concrete mixer trucks.        4. Better dust suppression is accomplished by elimination of the need to directly feed dry cementitious ingredients into mixer truck drums.        5. Generally cleaner mixer truck drums are seen, both inside and out, thereby simplifying clean out.        6. Material build-up on the back side of the truck mixer fins is reduced.        7. Both truck mixer head packs and cement balling in the load are eliminated.        
In recent years, attempts have been made to design equipment that would pre-mix the water and cementitious materials as part of the batching process before combining them with the aggregates. Such devices have been only partially successful.
One such approach has employed vortex-type mixers. Vortex mixers in some ways resemble home blenders. They include a large open-face pump at the base of each unit and a drain valve at the base of the pump which is situated above a charging hopper of a transit mixing truck as a final mixing vessel. The cementitious materials, water and some of the admixtures are introduced into the top of the vortex mixer. The ingredients are blended and thereafter, the valve at the base of the pump is opened and the mixed materials are transferred to the mixer truck where they are combined with aggregates. However, these units are limited to mix designs where the water/cement ratios are relatively high: 0.38 or greater. This may be higher than allowable for mixes designed to achieve low water/cement ratios. When this occurs, additional dry cementitious material must be added, handled separately from the rest of the cementitious material that is being blended in the vortex mixer, and charged directly into a truck. This is inefficient and may result in dusting problems.
Another device that has been used is a mixing tube employing a single screw mixing auger. In the single screw mixing auger, cementitious materials can be delivered to the mixing auger by various known methods. A water injection manifold is used to introduce the liquid materials into the cementitious materials as they are being conveyed through and by the screw auger. This type of pre-mixing device has had limited success due to an inability to overcome a variety of shortcomings which include:                1. Known units of this type have been unable to measure and control both the water and the cementitious material feeds in relation to each other so as to be able to blend these two in a known, selected, adjustable and repeatable manner.        2. The centrifugal action associated with the use of a single auger throws the materials being mixed outward and thereby forces the materials against and into water spray nozzles used to supply or infuse water into the mix causing them to plug and malfunction.        3. In addition, the action of the centrifugal force throwing the materials to the outside of the mixing tube results in incomplete mixing of the ingredients, as evidenced by the presence of streaks of dry cementitious material in the mix as it is discharged from the mixer.        4. Many single screw units experience a build-up of the mixed materials at the inlet where the cementitious materials and water begin to commingle due to insufficient baffling in this area.        5. Many single screw units also have difficulty mixing when the water/cement ratios are below 0.38.        
As is the case of the vortex-type mixers, some facilities using these units must also make provisions to handle additional dry cementitious material separately from the pre-mixed cementitious material and supply it directly into a truck or other final mixer vessel.
Thus, there remains a definite need in the concrete batching field to provide a concrete batching facility that includes a pre-mix arrangement that provides an accurate system to measure and control both the water and other wetting agents and the cementitious material feeds in relation to each other so as to blend the ingredients in a known, predetermined and repeatable manner over a relative wide range of ratios of water (wetting agent) to dry ingredients.